U.S. patent application number 10/230689 was filed with the patent office on 2004-03-04 for method and apparatus for read-only recovery in a dual copy storage system.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Gibble, Kevin Lee, Kishi, Gregory Tad, Patterson, David Lee.
Application Number | 20040044828 10/230689 |
Document ID | / |
Family ID | 31976557 |
Filed Date | 2004-03-04 |
United States Patent
Application |
20040044828 |
Kind Code |
A1 |
Gibble, Kevin Lee ; et
al. |
March 4, 2004 |
Method and apparatus for read-only recovery in a dual copy storage
system
Abstract
A system, apparatus, and method to recover a logical volume on a
read-only physical volume, or data storage cartridge, within a dual
copy data storage system, such as a virtual tape server (VTS)
system. The recovery follows a disaster situation involving the
primary physical volume and the requested logical volume. The
system, apparatus, and method include modules and steps as required
to recover a logical volume through recalling a selective dual copy
of the logical volume stored on a secondary physical volume. The
primary and secondary logical volumes are stored on distinct
physical volumes in order to provide quality storage media
management and reduce the likelihood of loss of data. The recovery
and recall procedures are implemented in a manner that is
substantially transparent and asynchronous to a host or client.
Additionally, the recovery and recall require no additional input
from the host in order to carry out the recovery of the logical
volume.
Inventors: |
Gibble, Kevin Lee; (Tucson,
AZ) ; Kishi, Gregory Tad; (Oro Valley, AZ) ;
Patterson, David Lee; (Tucson, AZ) |
Correspondence
Address: |
KUNZLER & ASSOCIATES
8 EAST BROADWAY
SALT LAKE CITY
UT
84111
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
Armonk
NY
|
Family ID: |
31976557 |
Appl. No.: |
10/230689 |
Filed: |
August 29, 2002 |
Current U.S.
Class: |
711/4 ; 711/162;
714/E11.101 |
Current CPC
Class: |
G06F 11/2058 20130101;
G06F 11/2056 20130101; G11B 20/1803 20130101; G11B 2220/41
20130101; G11B 2220/90 20130101; G06F 11/2087 20130101 |
Class at
Publication: |
711/004 ;
711/162 |
International
Class: |
G06F 012/16 |
Claims
What is claimed is:
1. A read-only recovery apparatus configured to recover a logical
volume on a physical volume, the apparatus comprising: a first
physical volume that is in a read-only status; an identification
module configured to identify a logical volume on the first
physical volume; a recall module configured to recall a selective
dual copy of the logical volume, the dual copy located on a second
physical volume; and the recall module further configured to recall
a volume construct associated with the logical volume.
2. The apparatus of claim 1, further comprising a reconciliation
module configured to update a storage manager server database to
synchronize a set of volume parameters in the database with a set
of attributes corresponding to the logical volume.
3. The apparatus of claim 2, further comprising a stripping module
configured to remove active data dependencies from the first
physical volume.
4. The apparatus of claim 2, further comprising a removal module
configured to remove the first physical volume from a data
management software inventory.
5. The apparatus of claim 1, wherein the recall module is further
configured to recover the logical volume in a manner that is
transparent to a host.
6. The apparatus of claim 5, wherein the recall module is further
configured to recover the logical volume in a manner that is
asynchronous with a host access to the logical volume.
7. The apparatus of claim 1, wherein the volume construct comprises
a storage group construct.
8. The apparatus of claim 1, wherein the volume construct comprises
a management class construct.
9. The apparatus of claim 1, wherein the second physical volume is
assigned to a storage pool that is distinct from the storage pool
to which the first physical volume is assigned.
10. The apparatus of claim 1, wherein the server is configured to
premigrate the logical volume to a different physical volume.
11. The apparatus of claim 1, wherein the server is additionally
configured to: re-evaluate the constructs of the logical volume;
determine if a selective dual copy is required; and re-create the
selective dual copy on a different physical volume.
12. A read-only recovery apparatus configured to recover a logical
volume on a physical volume, the apparatus comprising: a first
physical volume that is in a read-only status; an identification
module configured to identify a logical volume on the first
physical volume; a recall module configured to recall a selective
dual copy of the logical volume, the selective dual copy located on
a second physical volume; the recall module further configured to
recall a volume construct associated with the logical volume; the
recall module further configured to recover the logical volume in a
manner that is substantially transparent to a host and asynchronous
with a host access of the logical volume a stripping module
configured to remove active data dependencies from the first
physical volume; and a removal module configured to remove the
first physical volume from a data management software
inventory.
13. A virtual tape server capable of making selective dual copies
of a logical volume and configured to recover a logical volume on a
physical volume, the server comprising: a memory configured to
store computer code; the memory further configured to store active
data from the logical volume; a read-only recovery apparatus
configured to recover the selective dual copy of the logical volume
and a volume construct associated with the logical volume in
response to a notification that a first physical volume is in a
read-only status;
14. The server of claim 13, wherein the recovery apparatus is
further configured to recover the logical volume in a manner that
is transparent to a host.
15. The server of claim 13, wherein the recovery apparatus is
further configured recover the logical volume in a manner that is
asynchronous with a host access to the logical volume.
16. A read-only recovery method for recovering a logical volume on
a physical volume, the method comprising: identifying a logical
volume on a first physical volume that is in a read-only status;
recalling a selective dual copy of the logical volume, the
selective dual copy located on a second physical volume; and
recalling a volume construct associated with the logical
volume.
17. The method of claim 16, further comprising updating a storage
manager server database to synchronize a set of volume parameters
in the database with a set of attributes corresponding to the
logical volume.
18. The method of claim 17, further comprising removing active data
dependencies from the first physical volume.
19. The method of claim 17, further comprising removing the first
physical volume from a data management software inventory.
20. The method of claim 16, wherein recalling the selective dual
copy of the logical volume further comprises recovering the logical
volume in a manner that is transparent to a host.
21. The method of claim 20, further comprising recovering the
logical volume in a manner that is asynchronous with a host access
to the logical volume.
22. The method of claim 16, further comprising premigrating the
logical volume to a different physical volume.
23. The method of claim 22, further comprising: re-evaluating the
constructs of the logical volume; determining if a selective dual
copy is required; and re-creating the selective dual copy on a
different physical volume.
24. A dual copy storage system capable of making a selective copy
of a logical volume, the system comprising: means for identifying a
logical volume on a first physical volume that is in a read-only
status; means for recalling a selective dual copy of the logical
volume, which selective dual copy is located on a second physical
volume; and means for recalling a volume construct associated with
the logical volume.
25. A computer readable medium comprising a computer code
configured to carry out a read-only recovery method for recovering
a logical volume on a physical volume, the method comprising:
identifying a logical volume on a first physical volume that is in
a read-only status; recalling a selective dual copy of the logical
volume in a manner that is transparent to a host, the selective
dual copy located on a second physical volume; recalling a volume
construct associated with the logical volume; and updating a
storage manager server database to synchronize a set of volume
parameters in the database with a set of attributes corresponding
to the logical volume.
Description
BACKGROUND OF THE INVENTION
[0001] 1. The Field of the Invention
[0002] The invention relates in general to dual copy data storage
systems and more particularly to the read-only recovery of a
logical volume using a selective dual copy within a virtual tape
server (VTS) system in a manner that is transparent to and
asynchronous with a host.
[0003] 2. The Relevant Art
[0004] High density, removable media storage libraries are used to
provide large quantities of storage in networked computer systems.
Typically, such data storage systems are employed for backup or
other secondary storage purposes, but the data storage system may
also be used as primary storage in circumstances that are conducive
to sequential data access and the like.
[0005] The data is stored on media cartridges, such as magnetic
tapes or optical disks, that are arranged in storage bins and
accessed when data on a cartridge is requested. Currently available
media cartridges are capable of storing much more data than the
data volume units that correspond to the size of early types of
media cartridges. For example, a data volume that corresponds to a
400 megabyte disk may now be stored on a disk with up to 60
gigabytes of storage capacity. Unfortunately, much legacy equipment
in existing computer systems is configured for the smaller volume
sizes.
[0006] Volume mapping is used to create a correlation between the
physical capacity of a storage cartridge (stack volume or physical
volume) and the data storage unit size (virtual volume or logical
volume) of a file or block that is stored on the cartridge. Given
the available data storage capacity of a single storage media
cartridge, such mapping allows multiple logical volumes to be
stored on a single physical volume, hence providing an efficient
use of the available storage media. A virtual tape server (VTS) is
one device capable of creating and maintaining such mapping among
physical volumes and logical volumes.
[0007] A typical VTS system includes a virtual tape server and an
automated media library. The library is controlled by a library
manager that is similar to a workstation computer. Within the VTS
system, typically two databases reside on separate memory disks
within the system. One database resides on the virtual tape server
and the other resides within the library manager.
[0008] The virtual tape server database contains the
logical-to-physical volume mapping, as well as information
concerning volume attributes that define actions that have been or
will be taken on a logical volume each time it is closed. One of
the attributes included in such information is whether a secondary
copy of a logical volume was made when it was last written.
[0009] The library manager database also contains attributes
associated with the logical volumes stored on the media cartridges.
Included in these attributes are the construct names and associated
attributes corresponding to each logical volume in the library. The
library manager also controls the physical loading of media
cartridges in corresponding drives by storing the physical location
of the physical volumes within the storage bins and controlling a
robotic accessor arm that retrieves the physical volumes from the
bins and load the cartridges in the drives when a mount request is
received.
[0010] Through proper communication of the volume mapping and
construct attributes, a host processor and peripheral data storage
equipment may access logical volumes as though they were individual
physical volumes. The volume access management is provided via the
virtual tape server and library manager as described above.
[0011] In certain circumstances, it may be desirable to make two
copies of a single logical volume. It may also be desirable to
store such copies on multiple physical volumes, such as on separate
cartridges or even in separate geographic locations, so as to avoid
loss due to failure of a single tape or tape drive unit.
Additionally, it is desirable to provide a method of recovering the
secondary copy of the logical volume if, for some reason, the
primary copy becomes unavailable. Some systems and methods have
been proposed to recover a secondary copy of a logical volume in a
dual copy storage system. Unfortunately, a number of deficiencies
exist in such known systems and methods.
[0012] For example, many known dual copy systems require an
explicit command from the host to initiate recovery of a secondary
copy. The software running on the host must be modified to provide
the recovery command. As a result, such a recovery system may be
difficult to use with existing (legacy) software. Consequently,
adding recovery capability to an existing system may be rather
difficult. Prior art recovery systems may also require that the
host transmit the data to the virtual tape server repeatedly in
order to recover the secondary copy. Thus, the I/O resources of the
host are unduly taxed.
[0013] Furthermore, some dual copy systems require the host to
track the locations, i.e., the physical media cartridges, of the
logical volumes. This may require the maintenance of a special
database on the host to hold meta data for each file stored in the
virtual tape server. Again, such recovery systems are difficult or
impossible to incorporate into existing host systems without
providing new host software, and may unduly tax the resources of
the host. Additionally, such systems may be difficult to use in a
heterogeneous environment, i.e., with host computers that use
different operating systems, file formats, etc.
[0014] Thus, it would be an advancement in the art to provide a
virtual tape system capable of recovering a secondary copy of a
logical volume in a manner that is substantially transparent to the
host. It would further be an advancement in the art to provide a
virtual tape system capable of efficiently recovering a logical
volume independent of the host. Yet further, it would be an
advancement in the art to provide a virtual tape system that
minimizes the virtual tape server resources required to recover the
secondary copy.
BRIEF SUMMARY OF THE INVENTION
[0015] The present invention has been developed in response to the
present state of the art, and in particular, in response to the
problems and needs in the art that have not yet been fully solved
by currently available logical volume recovery means and methods in
dual copy data storage systems. Accordingly, it is an overall
objective of the present invention to provide a dual copy data
storage system and apparatus, as well as a read-only recovery
method that overcome many or all of the above-discussed
shortcomings in the art.
[0016] To achieve the foregoing objectives, and in accordance with
the invention as embodied and broadly described herein in the
preferred embodiments, a system, apparatus, and method for
recovering a logical volume in a dual copy storage system is
presented and described herein.
[0017] The read-only recovery apparatus, in the described
embodiments, is provided with a logic unit containing a plurality
of modules configure to carry out the individual steps of the
recovery process. These modules include an identification module, a
recall module, a reconciliation module, a stripping module, and a
removal module.
[0018] The read-only recovery apparatus is configured to implement
a recovery action to recover a selective dual copy of a logical
volume in response to a failure to access a primary logical volume.
The read-only recovery apparatus may employ the identification
module, the recall module, or the reconciliation module as part of
the recovery operations.
[0019] The identification module is configured to identify a
logical volume on a read-only physical volume. The recall module is
configured to recall a selective dual copy of the logical volume on
the read-only physical volume. Additionally, the recall module may
be configured to recall at least one volume construct associated
with the selective dual copy.
[0020] The reconciliation module is configured to update a storage
manager server database to synchronize a set of volume parameters
in the database with a set of attributes corresponding to the
logical volume. The reconciliation module may employ the stripping
module to remove active data dependencies from the first physical
volume and the removal module to remove the first physical volume
from a data management software inventory.
[0021] According to one embodiment, the virtual tape system
includes a virtual tape server (VTS) in communication with an
automated media library unit, including a plurality of tape drive
units and a library manager. The VTS receives the logical or
"virtual" volumes and stores them for subsequent transmittal to the
host, via a storage area network (SAN), or to a plurality of
physical or stack volumes via the tape drive units. The library
manager controls the physical loading of physical volumes, i.e.,
media cartridges, into the tape drive units by controlling a
robotic accessor arm that retrieves the physical volumes and loads
them into the tape drive units in response to a request from the
host.
[0022] The VTS has a direct access storage device (DASD) that may
exist on a hard drive system, or the like, and serve as a cache for
the VTS. Additionally, the VTS has a file system manager that
interacts with a DASD cache to store information.
[0023] Each logical volume has one or more constructs associated
with it, which are preferably received from the host. The
constructs may associate certain volume management actions with
specific logical volumes. The volume management actions preferably
specify at least where virtual volumes are physically stored,
including secondary locations if selective dual copying of the
volume is to be performed.
[0024] Upon notification to the VTS that a physical volume is in
read-only status, the system attempts to recover the secondary copy
of the logical volume and associated construct attributes. A
recovery module is employed to perform the volume recovery. The
physical volume may be assigned a read-only status due to physical
damage to the media cartridge or other error that prohibits full
access to the stored data.
[0025] A method of the present invention is also presented for
logical volume recovery when a primary physical volume is in
read-only status. The method attempts to access a primary logical
volume from a physical cartridge. When the VTS determines that the
primary volume is inaccessible or otherwise not retrievable in its
entirety, the VTS attempts to recover the selective dual copy of
the requested volume stored on a secondary physical volume.
[0026] To achieve the stated recovery, the virtual tape server in
one embodiment verifies the availability of a selective dual copy
of the logical volume. The method also allows for verification of
the status of the data on the logical volume. If the data is not
active data, then it is outdated and of no use to the host and need
not be recovered. If the data is active, on the other hand, the
method employs a recall procedure to recall the target logical
volume from the secondary physical volume. The recall procedure in
one embodiment also recalls construct attributes associated with
the selective dual copy of the logical volume, including a storage
group construct and a management class construct.
[0027] Following the successful recall of an active selective dual
copy, the method allows for reconciliation of the proper database
assignment and mapping data corresponding to the removed physical
volume, as well as any new location of the recovered logical volume
on new primary and secondary physical volumes.
[0028] These and other objects, features, and advantages of the
present invention will become more fully apparent from the
following description and appended claims, or may be learned by the
practice of the invention as set forth hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] In order that the manner in which the advantages and
objectives of the invention are obtained will be readily
understood, a more particular description of the invention briefly
described above will be rendered by reference to specific
embodiments thereof which are illustrated in the appended drawings.
Understanding that these drawings depict only typical embodiments
of the invention and are not therefore to be considered to be
limiting of its scope, the invention will be described and
explained with additional specificity and detail through the use of
the accompanying drawings in which:
[0030] FIG. 1 is a schematic block diagram illustrating one
embodiment of a representative virtual tape server (VTS) system in
accordance with the prior art;
[0031] FIG. 2 is a schematic block diagram illustrating one
embodiment of a representative virtual tape server suitable for use
with the VTS system of FIG. 1;
[0032] FIG. 3 is a schematic block diagram illustrating one
embodiment of a representative read-only recover apparatus in
accordance with the present invention;
[0033] FIG. 4 is a schematic flow chart diagram illustrating one
embodiment of a representative logical volume access method for use
in the present invention; and
[0034] FIG. 5 is a schematic flow chart diagram illustrating one
embodiment of a representative selective dual copy recovery for use
in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] Many of the functional units described in this specification
have been labeled as modules, in order to more particularly
emphasize their implementation independence. For example, a module
may be implemented as a hardware circuit comprising custom VLSI
circuits or gate arrays, off-the-shelf semiconductors such as logic
chips, transistors, or other discrete components. A module may also
be implemented in programmable hardware devices such as field
programmable gate arrays, programmable array logic, programmable
logic devices, or the like.
[0036] Modules may also be implemented in software for execution by
various types of processors. An identified module of executable
code may, for instance, comprise one or more physical or logical
blocks of computer instructions which may, for instance, be
organized as an object, procedure, or function. Nevertheless, the
executables of an identified module need not be physically located
together, but may comprise disparate instructions stored in
different locations which, when joined logically together, comprise
the module and achieve the stated purpose for the module.
[0037] Indeed, a module of executable code could be a single
instruction, or many instructions, and may even be distributed over
several different code segments, among different programs, and
across several memory devices. Similarly, operational data may be
identified and illustrated herein within modules, and may be
embodied in any suitable form and organized within any suitable
type of data structure. The operational data may be collected as a
single data set, or may be distributed over different locations
including over different storage devices, and may exist, at least
partially, merely as electronic signals on a system or network.
[0038] FIG. 1 illustrates a schematic block diagram of one
embodiment of a representative virtual tape system 100 in
accordance with the present invention. The system 100 includes an
automated library unit 102, at least one virtual tape server 104,
and at least one host 106. Each host 106 may be a mainframe
computer. Alternatively, the host 106 may be a server or personal
computer using a variety of operating systems. The host 106 and the
virtual tape server 104 are connected via a storage area network
(SAN) 108 or similar communications channel. The communications
channel 108 in one embodiment may be a FICON or ESCON.
[0039] The automated tape library unit 102 includes a library
manager 110, one or more data drive devices, which may be tape
drive units 112, an accessor 114, and a plurality of media
cartridges 116. The plurality of media cartridges 116 may be stored
in one or more media cartridge storage bins (not identified).
[0040] The library manager 110, which includes at least one
computing processor (not shown), is interconnected with, and
controls the actions of, the tape drive units 112 and the accessor
114. The library manager 110 typically also includes one or more
hard disk drives (not shown) for memory storage, as well as, a
control panel or keyboard (not shown) to provide user input. The
control panel may be a computer in communication with the library
manager 110 so that a user can control the operating parameters of
the automated tape library unit 102 independently of the host
106.
[0041] In FIG. 1, three tape drive units 112a, 112b, and 112c are
shown. The present invention is operable with one or any larger
number of tape drive units 112. The tape drive units 112 may share
one single repository of cartridges 116. Alternatively, the tape
drive units 112 may independently correspond to and utilize
multiple repositories of cartridges 116. The tape drive units 112
may advantageously be distributed over multiple locations to
decrease the probability that multiple tape drive units 112 will be
incapacitated by a disaster in one location.
[0042] The interconnections between the library manager 110, the
tape drive units 112, and the accessor 114 are shown as dashed
lines to indicate that the library manager 110 transmits and
receives control signals, rather than data to be stored or
retrieved, to the tape drive units 112 and/or the accessor 114.
Data for storage or retrieval may instead be transmitted directly
between the virtual tape server 104 and the tape drive units 112
via a network 118, which may be a storage area network (SAN), a
local area network (LAN), a wide area network (WAN), or a different
type of network, such as the Internet or a direct connection
between the virtual tape server 104 and the tape drive devices
112.
[0043] The accessor 114 may be a robotic arm or other mechanical
device configured to transport a selected cartridge 116 between a
storage bin and a tape drive unit 112. The accessor 114 typically
includes a cartridge gripper and a bar code scanner (not shown), or
similar read system, mounted on the gripper. The bar code scanner
is used to read a volume serial number (VOLSER) printed on a
cartridge label affixed to the cartridge 112. In alternative
embodiments, the tape drive units 112 may be replaced by optical
disk drives or other magnetic drives. Similarly, the cartridges 116
may contain magnetic media, optical media, or any other removable
media corresponding to the type of drive employed.
[0044] FIG. 2 illustrates a schematic block diagram depicting one
embodiment of the virtual tape server 104 of FIG. 1. The virtual
tape server 104 may take the form of a computer with a bus,
processor, memory, and the like. These elements have been omitted
from FIG. 2 to more clearly depict the various executable modules
and data blocks of the virtual tape server 104.
[0045] As shown, the virtual tape server 104 includes a file system
manager 202, a hierarchical storage manager 204, a storage manager
server 206, an automated storage manager administrator 208, and at
least one direct access storage device (DASD) cache 210. The DASD
cache 210 may take the form of one or more virtual tape drives to
contain data in the form of a logical, or virtual, volume 212. The
DASD cache 210 may also be the location where a database 214 for
the storage manager server 206 is stored. Other executable modules
and data blocks may also be present on the DASD cache 210, but are
omitted to focus on the present invention.
[0046] The file system manager 202 handles the actual DASD 210 read
and write commands from the host 106, in one embodiment, via the
hierarchical storage manager 204. The storage manager server 206
controls the interface communications between the DASD 210 and the
drive devices 112. The storage manager server 206 is controlled by
the automated storage manager administrator 208. The automated
storage manager administrator 208 monitors and directs the
operation of the file system manager 202, the hierarchical storage
manager 204, and the storage manager server 206, and communicates
control information to and from the library manager 110.
[0047] The DASD cache 210 is used to hold a plurality of logical,
or virtual, volumes 212 from the physical volumes, or memory
cartridges 116. A read or write command from the host 106 is
processed by the virtual tape server 104 via the DASD 210 prior to
transferring the updated logical volume 212 from the DASD cache 210
to the physical volume 116.
[0048] The transfer of the updated logical volume 212 from the DASD
cache 210 to a physical volume 116 may occur in a variety of ways.
In one embodiment, the logical volume 212 resident on the DASD
cache 210 may be the only copy of that logical volume 212. At a
time determined by the virtual tape server 104, the logical volume
212 maybe premigrated to a physical volume 116. Such volume
premigration provides for the virtual tape system 104 to make a
copy of the logical volume 212 resident on the DASD cache 210 and
store it on a physical volume 116. The principal copy of the
logical volume 212 remains on the DASD cache 210 for potential
accesses by the host 106.
[0049] If the host 106 does not access the logical volume 212 on
the DASD cache 210 within a certain time frame, the virtual tape
server 104 may decide to complete the migration of the logical
volume 212 to the physical volume 116. In this instance, the
virtual tape server 104 insures that the copy on the physical
volume 116 is the most recent, or active, data and removes the
logical volume 212 from the DASD cache 210 to provide memory for
other data as required.
[0050] The virtual tape server 104 illustrated also includes a
read-only recovery module 216 that is configured to recover a
selective dual copy of a logical volume that is on a read-only
physical volume.
[0051] Referring to FIG. 3, a schematic block diagram illustrates
one embodiment of a read-only recovery module 302 given by way of
example of a read-only recovery module 216 as shown in FIG. 2. The
read-only recovery module 302 depicted includes an identification
module 304, a recall module 306, and a reconciliation module
308.
[0052] The identification module 304 is configured to identify a
logical volume 212 on physical volume 116. In one embodiment, the
identification module 304 may be further configured to identify the
location of a selective dual copy of the logical volume 212 that is
located on a separate and distinct physical volume 116. The
selective dual copy of the logical volume 212 may be referred to as
a backup copy of the logical volume 212. Identification of these
logical volumes 212, their locations on respective physical volumes
116, and attributes associated with each logical volume 212
provides the virtual tape server 104 with at least some of the
information necessary to recall the selective dual copy of the
logical volume 212 when the primary copy may become unavailable,
either temporarily or permanently.
[0053] The recall module 306 is configured to recall the selective
dual copy of the logical volume 212 to the DASD cache 212 of the
virtual tape server 104 when the primary logical volume 212 is on a
read-only physical volume 116 that is inaccessible. A physical
volume 116 may be placed in a read-only state when the VTS system
100 is unable to access part or all of the information stored on
the media cartridge 116. Such inaccessibility is very likely to be
due to physical damage or wear on the cartridge 116 that may not be
reparable.
[0054] The VTS system 100 may attempt to recover information from
the primary physical volume 116 using multiple techniques commonly
known in the preset art. Among these techniques are switching media
drives 112, reverse-reading, and the like. Following this attempted
recovery, the read-only recover module 302 may, in one embodiment,
employ the recall module 306 to recall the selective dual copy of
any or all logical volumes 212 not presently recovered from the
primary physical volume 116.
[0055] The reconciliation module 308 is employed by the read-only
recovery module 302 following a successful recovery of at least one
logical volume 212 or portion thereof. The reconciliation module
308 in one embodiment includes a stripping module 310 and a removal
module 312.
[0056] The stripping module 310 is configured to remove active data
dependencies from the read-only physical volume 116 following a
successful recall of at least some of the data on the physical
volume 116. The removal module 312 is configured to remove
reference to the physical volume 116 from which the data has been
recovered from a data management software database of physical
volume 116.
[0057] Referring to FIG. 4, a schematic flowchart diagram depicts
one embodiment of a logical volume access method 400 that may be
employed by the VTS system 100. The method 400 starts 402 by
querying 404 the storage manager server 106 within the virtual tape
server 104 for a list of physical volumes 116 that are indicated as
read-only. The method 400 continues with the selection of one of
the read-only physical volumes 116 and further selection 406 of a
logical volume stored on the selected physical volume 116. The
selected logical volume 212 may be identified by a corresponding
VOLSER that is unique to the logical volume 212.
[0058] Having identified a target logical volume 212 that the
virtual tape server 104 attempts to access, the virtual tape server
104 in one embodiment determines 408 if a copy of the identified
logical volume 212 is resident on the DASD cache 210. If a copy of
the identified logical volume 212 is resident on the DASD cache
210, the virtual tape server 104 determines 410 if the logical
volume 212 on the DASD cache 210 is a premigrated copy. A copy of
the logical volume 212 that is not premigrated is assumed to be
active data (the most recent copy of the logical volume) and the
method 400 ends 412.
[0059] A copy of the logical volume 212 that is a premigrated copy
may be marked 414 as an active copy. Alternately, it may be assumed
that the premigrated copy of the logical volume 212 that resides on
the DASD cache 210 is active data. In either case, the logical
volume access method 400 ends 412.
[0060] If it is determined 408 that a copy of the target logical
volume 212 is not resident on the DASD cache, the virtual tape
server 104 attempts to access 416 a copy of the logical volume on
the primary physical volume 116 that is indicated to be in a
read-only state. If such access is determined 418 to be successful,
for example if the logical volume 212 on the physical volume 116 is
accessible, the virtual tape server recalls 420 the logical volume
212 or accessible portions thereof to the DASD cache 210. Any data
recalled at this point is marked 422 as active data and the
database 214 of the storage manager server 206 is reconciled 424 as
discussed previously. The method 400 then ends 412.
[0061] If it is determined 418 that the logical volume 212 on the
physical volume 116 is not accessible, the read-only recovery
module 302 attempts to recover 426 the selective dual copy of the
logical volume 212. The method 400 then ends 412.
[0062] Referring to FIG. 5, a schematic flowchart diagram depicts
one embodiment of selective dual copy recovery method 500 given by
way of example of a selective dual copy recovery step 426 of FIG.
4. The method 500 begins 502 as the recall module 306 of the
recovery module 302 accesses 504 the selective dual copy of the
logical volume 212 on the secondary physical volume 116.
[0063] After the recall module 306 accesses 504 the selective dual
copy, the recovery module 302 determines 506 if the data in the
selective dual copy is active data. If it is determined 506 that
the selective dual copy does not contain active data, the selective
dual copy recall and recovery fails 508 and the method 500 ends
510. A selective dual copy of a logical volume 212 that does not
contain active data is of no use to the host 106 because some or
all of the information has been superceded by revised or new
data.
[0064] If it is determined 506 that the selective dual copy does
contain active data, and is therefore the data requested by the
host 106, the recovery module 302 recalls 512 the selective dual
copy of the logical volume 212 and stores it in the DASD cache 210
of the virtual tape server 104. The recalled logical volume 212 now
residing in the DASD cache 210 is marked 514 as active data ready
to be accessed by the host 106. At a time determined by the virtual
tape server 104, the logical volume 212 may be premigrated or
migrated to at least one physical volume 116, as described
previously.
[0065] In one embodiment, at a time determined by the virtual tape
server 104, the virtual tape server 104 reevaluates the constructs
associated with the logical volume 212 to determine if the logical
volume still requires a selective dual copy. The logical volume 212
is premigrated or migrated to at least one physical volume 116, as
described previously. In some implementations, if a selective dual
copy is required, the logical volume 212 is premigrated or migrated
to at least one other physical volume 116, as described
previously.
[0066] Once the selective dual copy of the logical volume 212 is
recalled 512 and marked 514 as active data, in one embodiment, the
database 214 of the storage manager server 206 is reconciled 516 in
a manner similar to that of step 424 and the method 500 ends
510.
[0067] The present invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. The described embodiments are to be considered in
all respects only as illustrative and not restrictive. The scope of
the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
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